This invention relates to selective soldering and, in particular, to electrical and mechanical attachment of connectors to printed circuit boards (PCBs).
In the fabrication of circuit packs, electrical connectors are usually mounted on one edge of a printed circuit board. The connectors typically include either pins or pin-receiving receptacles within a housing and tail portions extending therefrom which must be electrically connected to pads on the circuit board. This connection is usually achieved by soldering the tails to the pads. (See, e.g., U.S. Pat. No. 5,080,722 issued to Englert et al.)
One method of soldering components in general involves applying a flux and solder to the piece part and, subsequently, cleaning off the excess material. (See, e.g., U.S. Pat. No. 4,720,324 issued to Hayward and U.S. Pat. No. 4,306,674 issued to Charles et al.) The cleaning, however, generally requires the application of chlorofluorocarbon (CFC), such as FREON.RTM., which is harmful to the environment. While alternative cleaning techniques have been proposed (see Patent to Englert et al. cited above), it is also desirable to eliminate the cleaning step altogether.
One approach to no-clean soldering is to apply the flux in a carefully controlled manner by spraying the entire board and then apply solder by wave soldering. Since only the amount required to ensure a good solder connection is applied, no cleaning is required. (See L. A. Guth and J. R. Morris, "No-Clean Soldering Processes," AT&T Technical Journal, pp. 37-44 (March/April 1992).
While such an approach is adequate for soldering components in general to PCBs, attachment of connectors to PCBs present special problems since the PCB pads are usually close to the connector housing and it is generally required to keep flux out of the housing.